Gallium Nitride (GaN) Based Transistors Jason Ross – Physics Santa Barbara City College Mentor: Nidhi Faculty Advisor: Umesh Mishra Department of Electrical and Computer Engineering UCSB Funded by:
The Transistor Gate e - flow � Amplifier � Switch Mishra, U. Eastman, L. Toughest Transistor Yet, IEEE, Volume 39 May 2002 Source Drain Gate Why GaN? • Forms 2D Electron Gas (2DEG) GaN making it a High Electron Mobility Transistor (HEMT) AlGaN • Tough • High Thermal Conductivity • High Breakdown Voltage
Why Do the Research? They Are Everywhere : � Computers � Stereos and TVs � Wireless Internet � Communication Infrastructure � Hybrid Electric Cars � The Electric Grid � Defense Satellites and Radar
Gate e - flow Research Goals Bring Out GaN Advantages: Transistor Design � Handle High Voltages (Fabrication) � Perform at High Frequencies Examples � Self Aligned Gate Characterize Transistors � Measure Electron Velocity � Determine Electron Mobility
The Fabrication Process Material Photolithography Annealing Deposition UV Light 870 o C Plasma Drain/Sourc Mask e Photoresist (PR) PR e - beam Wafer Gold GaN
Self Aligned Gate Design Gate Advantages: SiO 2 Drain Source Cr • Reduces distant between source and drain resulting in a W n++ small, fast device (Great high GaN frequency performance). AlGaN • Reduces contact resistance GaN with highly Silicon doped GaN terminals. Sapphire
Transmission Line Measurement (TLM) Purpose : V Measure e - Velocity R c w And Mobility AlGaN GaN Analysis : Current = qn s v E = (V – IR c )/w q = e - charge I = current n s = charge density v = e - velocity
TLM Results 9.4x10 6 cm/s 1300 cm 2 /Vs 7 1.0x10 6 7.5x10 Velocity (cm/s) Spacing (w) 6 5.0x10 3 micron 5 micron 8 micron 12 micron 6 2.5x10 20 micron 0.0 0.0 4 4 4 3.0x10 6.0x10 9.0x10 Electric Field (V/cm)
In Perspective Mobility: 1300 cm 2 /Vs Velocity: 9.4x10 6 cm/s Test: 3 micron Target: <100nm Mishra, U. Eastman, L. Toughest Transistor Yet, IEEE, Volume 39 May 2002
Future Plans Gate • Improve regrowth process. SiO 2 Drain Source Cr • Use Indium Nitride for the terminals. W AlGaN • Develop methods for better measurement of sidewall thickness and quality. GaN Sapphire • Compare results to Nitrogen faced design.
Summary Accomplishments : • Learned and help perform fabrication processes in clean room. • Gained knowledge of semiconductor device physics. • Performed tests and collected valuable data on transistor performance. • Gained communication and technical skills. • Learned what graduate research is like.
Acknowledgements Nidhi Umesh Mishra INSET and CNSI Our Sponsors The Nanofab
Thank You!
Self Aligned Gate Process Goals: UV Light • Reduce resistivity with Mask highly doped GaN Photoresist (PR) PR terminals. Chromium (Cr) Gate Cr Drain Source SiO 2 SiO 2 • Bring Source and Drain Chromium (Cr) Cr close together resulting n++ in a very fast device GaN Tungsten (W) W (great high frequency SiN x performance) AlGaN GaN Process: Photolithography Deposition Regrowth Etching Sapphire
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